(1) Field of the Invention
This invention relates to the casting of metal strip articles by means of continuous strip casting apparatus of the kind that employs continuously moving elongated casting surfaces and side dams that confine the molten and semi-solid metal to the casting cavity formed between the moving casting surfaces. More particularly, the invention relates to such apparatus in which strip articles of variable width may be produced.
(2) Description of the Related Art
Metal strip articles (such as metal strip, slab and plate), particularly those made of aluminum and aluminum alloys, are commonly produced in continuous strip casting apparatus. In such apparatus, molten metal is introduced between two closely spaced (usually actively cooled) elongated moving casting surfaces forming a narrow casting cavity. The metal is confined within the casting cavity until the metal solidifies (at least sufficiently to form an outer solid shell), and the solidified strip article is continuously ejected from the casting cavity by the moving casting surfaces and may be produced in indefinite length. One form of such apparatus is a twin-belt caster in which two confronting belts are circulated continuously and molten metal is introduced by means of a launder or injector into a thin casting cavity formed between the confronting regions of the belts. An alternative is a rotating block caster in which the casting surfaces are formed by blocks that rotate around a fixed path and join together adjacent the casting cavity to form a continuous surface. The metal is conveyed by the moving belts or blocks for a distance effective to solidify the metal, and then the solidified strip emerges from between the belts at the opposite end of the apparatus.
In order to confine the molten and semi-solid metal within the casting cavity, i.e. to prevent the metal escaping laterally from between the casting surfaces, it is usual to provide metal side dams at each side of the apparatus. For twin-belt and rotating block casters, side dams of this kind can be formed by a series of metal blocks joined together to form a continuous chain aligned in the casting direction at each side of the casting cavity. These blocks, normally referred to as side dam blocks, are trapped between and move along with the casting surfaces and are recirculated so that blocks emerging from the mold exit move around a guided circuit and are fed back into the entrance of the mold. The blocks are guided on this circuit by means of a metal track, or the like, on which the blocks can slide in a loose fashion that allows for limited movement between the blocks, especially as they move around curved parts of the circuit.
When casting strip articles in this way, it is often desirable to produce strip articles of different lateral widths for different purposes. When using the conventional arrangement, this involves terminating the casting operation after the completion of casting of a product of a first width, and re-configuring the caster for the production of a strip article of a second width. For example, it may be necessary to replace one metal injector for a different one of different width, and to move the side dam blocks correspondingly towards or away from the center line of the casting surfaces (which involves moving the entire circuit for recirculating the side dam blocks through the casting cavity and around the external circuit). As this is cumbersome and time-consuming, it would be desirable to provide a system or arrangement for facilitating the change-over of the casting equipment when strip articles of different widths are to be produced.
U.S. Pat. No. 6,363,999 issued to Dennis M. Smith on Apr. 2, 2002 discloses a molten metal injector used with a twin roll caster (in which the metal is cast within the nip formed between the rolls) rather than a twin belt or moving block type caster in which the casting cavity is formed between elongated casting surfaces. The injector is provided with end dams along its sides and these are adjustable towards or away from the center line of the nip. However, the end dams do not extend beyond the nozzle of the molten metal injector.
U.S. pending patent application No. US 2008/0115906, published on May 22, 2008 naming Oren V. Peterson as inventor, describes a metal casting apparatus for steel in which molten metal is poured onto a single moving belt, where it at least partially solidifies, before it is conveyed onto a run-out table on which the solidification process is completed. The apparatus has movable side walls for laterally containing the molten metal and that can be adjusted to produce slabs of different widths. However, there is no upper casting surface and the molten metal is merely poured onto the lower belt rather than being injected from an entrance to a casting cavity.
Other references having side dam arrangements are disclosed, for example, in U.S. Pat. No. 3,063,348 issued on May 29, 1962 to Hazelett et al., U.S. Pat. No. 4,727,925 issued on Mar. 1, 1988 to Asari et al.; Japanese patent application No. JP 60-049841 published on Mar. 19, 1985, and Japanese patent application No. JP 61-0132243 published on Jun. 19, 1986.
There is a need for improved arrangements that can, in particular, make it possible to cast strip articles of different widths without terminating casting operations.